The present invention relates to a rotation sensor such as a vehicle wheel speed sensor or an engine revolution sensor.
FIG. 9 shows a conventional wheel speed sensor P. It includes a detector X mounted on a circuit board 3 which is in turn carried on a resin holder 2. With the detector X mounted on the holder 2, the holder 2 is inserted into a cylindrical casing 1 having open and closed ends from its open end 1a until a base portion 2a of the holder 2 closes the open end of the casing 1. A pair of lead wires 9 extending from the detector X are each connected to one of a pair of relay terminals 5 which extend through the base portion 2a of the holder 2 and protrudes from its outer end face. The relay terminals 5 have their protruding ends connected to an output cable 6. A cover 4 is formed by molding a resin to completely conceal the portion of the holder 2 protruding from the open end 1a of the casing 1 and to embed therein the protruding ends of the relay terminals 5 and the portion of the cable 6 connected to the terminals 5.
The detector X typically comprises an IC chip for detecting magnetic fields and electronic parts (circuit) for controlling (as disclosed in JP Patent publication 2002-257840, FIG. 4) or comprises an electromagnetic pickup including a pole piece provided inside of a bobbin on which a coil is wound, and a magnet provided rearwardly of the pole piece (as disclosed in the above publication, FIG. 1).
As shown in FIG. 9, the wheel speed sensor P is mounted on a mounting member A with its detector X opposing a rotary member B to be detected. The detector X picks up any change in the magnetic field produced from the rotary member B when the rotary member B rotates, and converts the change in the magnetic field to electrical signals which are transferred to a control device through the relay terminals 5 and the output cable 6. The rotary member B is a ferromagnetic pulse ring having teeth similar to gear teeth on the radially outer periphery thereof, or a magnet pulse ring having its radially outer periphery magnetized such that North poles and South poles circumferentially alternate with each other.
As today's motor vehicles are increasingly sophisticated, it is necessary to densely pack various devices and components, besides wheel speed sensors, in a limited space. Thus, smaller wheel speed sensors are required. To reduce the size of a wheel speed sensor, its components have to be arranged closer to one another. This increases the possibility of interference of each component with other components and poses other problems.
For example, pressure produced when forming the resin cover 4 tends to have a detrimental influence on the detector X. Specifically, when forming the cover 4 by molding a resin, pressure is applied through a flange 1b of the casing 1 to the holder 2 as shown by the arrow in FIG. 9. This tends to cause the base portion 2a of the holder 2 to bulge in the axial direction in the casing 1. The relay terminals 5 are thus pushed in the axial direction too, thus detrimentally influencing an electronic part 8 and a rotation sensor element 7, namely, lowering the detection accuracy.
One possible way to protect the electronic part 8 and the sensor element 7 would be to provide each relay terminal 5 with a bent portion 5a as shown in FIG. 9 so that the bent portions 5a can absorb any axial pushing force applied to the relay terminals 5.
But in order for the bent portions 5a to sufficiently absorb such axial pushing force, they have to have their both ends fixedly supported by stationary, fixed members or portions.
In this regard, in the arrangement of FIG. 9, each bent portion 5a is connected to one of a pair of flexible, insulated or bare lead wires 9. That is, each bent portion 5a is not fixedly supported by a stationary, fixed member or portion at least at one end thereof. Thus, the bent portions 5a cannot sufficiently absorb any axial pushing force applied to the relay terminals 5. Such axial force is mostly absorbed by the flexible lead wires 9 instead. However, in the arrangement of FIG. 9, since the lead wires 9 are not directly connected to the sensor element 7 or the electronic part 8, any axial pushing force applied to the relay terminals 5 will not be transmitted to the sensor element 7 or the electronic part 8 even without the bent portions 5a. Thus, the bent portions 5a do not serve to protect the sensor element 7 or the electronic part 8 from axial pushing force applied to the relay terminals 5.
In order to answer the requirements for compactness, many of today's rotation sensors X do not include the circuit board 3 shown in FIG. 9 In this arrangement, a pair of lead pieces, which carry an electronic part, extend directly from the sensor element 7 in parallel to each other, and the relay terminals 5 are directly connected to the respective lead pieces.
In this arrangement, since the lead pieces are directly connected to the sensor element 7, any axial pushing force applied to the relay terminals 5 tends to be transmitted to the sensor element 7, thus detrimentally influencing the sensor element 7.
An object of the invention is to minimize transmission of any axial pushing force applied to the relay terminals when the cover 4 is formed to the detector X.